Not sure I'd really know how to "be open with people", I guess it just happens if I trust the person enough.
If I tell someone about my AS, though, it means I trust them. But I've told verrrrrry few NTs. If anyone asks about my special needs, I'll say I want to keep it private (or hint at that by just saying "I've got something"), and will generally only say I have dyspraxia if I have to tell them.
However, I don't hide it if someone asks me. If someone asks me if I have AS/autism, I'll tell them so, because they clearly have taken time to learn what those things are instead of taking the Rain Man stereotype.
But, I'm going on a tangent.
The main point to make when it comes to being open is that I have no idea what I'm feeling about most things - my emotions are somehow disconnected from my brain. I can work them out by analyzing things in my head or by writing poetry. I usually do the former, which takes months.
So, if I trust someone enough, I'll be likely to share with them what I know. And maybe I'll work things out as I'm talking to them, too. And I won't lie about things concerning emotions either. But I can't be fully open because I don't know how.